World No. 1,207 Derek Ernst claimed the Wells Fargo Championship in a play-off on Sunday, after a rain-soaked day that saw a host of more established names fall by the wayside.

Ernst eventually defeated Englishman David Lynn at the first sudden death hole to claim his maiden professional victory in his first season on the PGA Tour, tapping in for a par at the treacherous 18th after Lynn had only managed to fumble his way to a bogey.

"This feeling is unbelievable right now," Ernst said.

But before that both players had seen long-time leader Phil Mickelson fall apart; the left-hander succumbing down the so-called 'Green Mile' - the immensely difficult final three holes at Quail Hollow - to drop two shots and fall from the outright lead to outside the play-off.

Mickelson finished seven-under for the tournament after a closing round of 73, ending up with scant reward for a day where he struggled manfully in horrible conditions to try and claim victory. After throwing away his lead with mistakes at the 16th and 17th he managed to rally enough to give himself the birdie opportunity he required at the last (the hardest hole on the course), but his decisive putt slipped agonisingly past.

"I felt like I was in control, and I let it slip away there the last few holes, so it was disappointing," Mickelson said afterwards.

That left Ernst and Lynn, two players who had finished long before on a day where play was pushed forward due to an atrocious weather forecast. Playing driving rain throughout the pair, the duo carded matching fourth rounds of 70 to both sit at eight-under and end up in one of the most unlikely play-offs of the year.

After both players had safely avoided trouble at the water-lined last, Ernst fired his approach shot to 15 feet as Lynn found a greenside bunker. The Englishman then bladed his escape attempt over the other side of the green - condemning himself a bogey and allowing his opponent two putts for the win.

Those Ernst would take, ensuring his world ranking come Monday morning will be markedly higher. Originally the fourth alternate to even get into the field for the event, Ernst previously came through all four rounds of Q-School to earn his playing privileges on the PGA Tour for this season.

Elsewhere, Lee Westwood finished inside the top five, although it looked like potentially being so much better when the Englishman moved to eight-under for the tournament at the 14th. Unfortunately, he was another to fall victim of the 'Green Mile', dropping shots at 16 and 17 to eventually slide back to six-under after a level-par closing round.

World No. 2 Rory McIlroy, meanwhile, saw his own hopes of victory fall apart at the 12th - as he stumbled to a double-bogey. After dropping a shot at the first, the Northern Irishman picked up three shots before the turn to put himself firmly in contention - but dropped shots at 13 and 18, after that disaster at 12, meant he finished the tournament four-under after a closing round of 73.